Processes for the continuous casting of molten metal and the detection of the level of the metal in a mold cavity are known in the prior art.
According to one known process, described in French Pat. No. 2,296,482, molten metal is passed continuously to the inlet of a molding cavity, which may be formed by a pair of moving belts, one belt being located above the other, and a pair of side dams, and the casting process is controlled by the generation of a plurality of signals indicative of the level of the molten metal at the inlet. To this end, in the French patent, several signals are generated by means of heat detectors which are held against the moving belts. The heat detectors are arranged in two series and the apparatus for carrying out the process also includes a device for treatment of the signal from the detectors and a command device.
According to other known processes, referring to U.S. Pat. Nos. 3,459,949 to P. Poncet and 3,838,727 to I. Levi et al, there is also disclosed, in a process for the casting of steel, a system for detection of the level of the molten metal in a mold. Detection is by means of an optical system located outside a molding cavity to expose a photosensitive element in an optical path directed at a field extending on opposite sides of a line of demarcation between the surface of the metal and the wall of the cavity. These patents generally are similar in that they disclose a process for casting steel in a vertical mold with fixed walls and that casting control is achieved by a signal generated by the photosensitive element which is a function of the radiation generated within the field.
A further patent of the prior art, namely U.S. Pat. No. 2,246,907 to W. R. Webster, also discloses an apparatus for the continuous casting of metal. As described in the patents immediately above, the casting process is carried out in a vertical mold, the walls of which are capable of movement, including a quartz rod disposed within and at a predetermined distance below the top of the mold for transmission of radiation to a photosensitive element.
The processes and apparatus of the prior art suffer from various problems and disadvantages. Thus, the process and apparatus of Webster including the photosensitive element which is not exposed to radiation through an optical system located outside of the mold cavity, suffers from the requirement that the quartz rod need be located within the inlet to the mold cavity in the neighborhood of the surface of the molten metal. In this disposition, because of soiling by metal projections, the quartz rod may become unsuitable for transmission of radiation.
As to the casting process and apparatus described by each of Poncet and Levi et al, it is carried out in a mold cavity defined by fixed walls rather than in a mold cavity defined by movable walls. And, the control means of each patent could not be adapted for implementation in a movable wall mold cavity. Considering the apparatus of the French patent, it is relatively complicated both in structure and operation since the treatment device must treat a relatively large number of signals deriving from the plural detectors and the signals are a function of heat rather than light essentially in the visible spectrum.